Preferential low-pH dissolution of pyroxene in plagioclase-pyroxene mixtures: Implications for martian surface materials

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2008.01.008 Byline: Amy C. McAdam (a), Mikhail Yu. Zolotov (a), Thomas G. Sharp (a), Laurie A. Leshin (b) Keywords: Mars; surface; Mineralogy Abstract: Acid weathering of plagioclase-pyroxene mixtures has been investigated with an open system kinetic dissolution model. The modeling reveals that elevated plagioclase/pyroxene ratios observed in some low-albedo martian regions and atmospheric dust could be partially caused by preferential dissolution of pyroxenes at pHs below [approximately equal to]3-4. Surface materials with smaller grain sizes, affected by lower pH fluids, and/or exposed to longer durations of acid weathering would be enriched in plagioclase. If preferential dissolution is responsible for the observed mineral ratios, the dissolution process likely occurred on a large scale, such as weathering by acid atmospheric precipitates. If dissolution was continuous, modeled timeframes required to produce a high plagioclase/pyroxene ratio are short on geologic timescales; however, it is likely that acid weathering on Mars was episodic, possibly occurring over a longer period of time. Author Affiliation: (a) School of Earth and Space Exploration, Arizona State University, Box 871404, Tempe, AZ 85287-1404, USA (b) Sciences and Exploration Directorate, Code 600, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA Article History: Received 5 June 2007; Revised 29 December 2007